When used for electronic imaging, charged coupled devices referred to as CCDs often require precisely positioned pulses with respect to the horizontal clock signal by using a delayed leading edge. These pulses are produced in response to an input square wave clock signal. For example, a buffer amplifier on a CCD sensor is used to sense the voltages of a floating diffusion. The floating diffusion needs to be reset before the charge is transferred by the next clock cycle. The required pulse, known as a reset pulse, is generated by a precisely delayed leading edge of the square wave signal. Additionally, the output amplifier of the CCD is sampled, held and compared to a charge level on the floating diffusion. The sample and hold also needs precisely positioned pulses. The output amplifier can be controlled also by a timed delayed square wave. In CCD sensors, it is essential that a circuit be provided that has facility of precisely delaying a square wave signal which is used to generate the precisely positioned pulses into required pulsewidth, as well as producing pulses which are precisely positioned and which have a predetermined pulse width.
The classical way of generating such pulses (which are of high frequency in the order of 10-20MHz) is done by means of fixed timed delayed chips and combinatorial logic. This approach is expensive, and very difficult to change the precisely positioned pulses. The required timed delay can also be achieved by resistor capacitor circuits but it is difficult to lengthen delay time and also produce required pulse widths with such circuits.